This study investigates the relative value of a high monounsaturated fat diet & a low-fat diet in subjects with noninsulin-dependent diabetes mellitus (NIDDM) treated with sulfonylureas and metformin, utilizing both isocaloric and self-selected periods of diet therapy. This approach will test the hypothesis that monounsaturated fats improve the metabolic abnormalities of NIDDM, including glucose control, insulin sensitivity and lipid abnormalities.